1. given the following full electron configuration, which is the noble gas electron configuration? → 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2
a. [ar] 4s^2
b. [mg] 3p^6 4s^2
c. [ne] 3s^2 3p^6 4s^2
d. [ne] 4s^2
( i am so lost)

The element identified in the original electron configuration is Calcium, Ca, so move backwards from there. The noble gas you reach first is Argon. For the noble gas configuration, you'd use Argon and then 4s^2 to acknowledge that it's still Calcium that the electron configuration is identifying.

The answer is A, [Ar] 4s^2.

Let me know if you need more of an explanation on electron configuration itself.

1. for the first question, we must find the mass of the anhydrous salt, mgso₄. the molar mass for mgso₄·7h₂o is 246.47 g/mol, while that of mgso₄ is 120.37 g/mol.7.834 g mgso₄·7h₂o * 1 mol mgso₄·7h₂o/246.47 g * 1 mol mgso₄/1 mol mgso₄·7h₂o * 20.37 g mgso₄/mol = 0.647 g mgso₄

2. mass of water = mass of sample - mass of anhydrous salemass of water = 7.834 - 0.647 = 7.19 gpercent water in hydrate = 7.19/7.834 * 100 = 91.74%